1. Field of the Invention
The present invention relates to an improved method and system for removing contaminants from synthetic resin materials, such as plastic. More particularly, the present invention relates a resin recycling method and system that produces essentially contaminant-free synthetic resin material in an environmentally safe and economical manner.
2. Description of the Prior Art
Recycling containers made from synthetic resin material is a highly desirable alternative to landfilling such containers. However, these containers often include residues of the material they once contained. These residues if not removed can decrease the value of the container material making it suitable for only low-grade products. Traditionally, these residues or contaminants have been difficult and expensive to remove and prone to create additional waste byproducts.
Recycling of motor oil containers is illustrative of the problem. Motor oil containers typically are high-density polyethylene (HDPE) which lends itself well to recycling if it is sufficiently clean. However, residual oil coating the interior surface of the “empty” motor oil containers constitutes a contaminant that prevents re-use of the containers in at least a high grade plastic application, such as the packaging of food or beverages.
The aforementioned problem is not just limited to oil containers. Similar contamination problems exist for example with pesticides from HDPE containers, milk from HDPE containers, “soda water” from polyethylene terephthalate (PET) containers, polychlorinated biphenyl (PCB) contaminants particularly from automotive plastics, and contaminants from various other post-consumer containers, such as detergent containers, collected from curbside recycling programs.
The significant amount of the above mentioned types of containers are currently disposed of in landfills, leaking oil and other contaminants into the soil and groundwater, and occupying significant landfill volume.
Several known options exist other than landfilling the waste synthetic resin containers, including (a) grinding the containers and using them in other recycling processes on a very limited (dilute) basis; (b) using an aqueous process to displace the contaminant from the synthetic resin material; (c) using a halogenated solvent to dissolve/dilute the contaminant; or (d) using a combustible or flammable solvent to dissolve/dilute the contaminant oil from the synthetic resin material.
The problems with these options are as follows:
Existing recyclers in the United States can blend limited quantities of contaminated synthetic resin materials in recycled products. Large quantities cannot be blended because of the undesirable effects of the contaminants on the recycled synthetic resin material properties. Examples include “plastic lumber” and lower grade plastic products.
Aqueous processes can be used to displace the contaminants from the synthetic resin material. However, detergents and/or surfactants are required to assist displacement of the contaminants. A stream of usable contaminant-free synthetic resin material will be generated by this method; however, the displaced contaminants will need additional processing to separate them from the aqueous solutions or dispersions. The aqueous solutions or dispersions themselves will be a secondary waste stream that will require treatment before being recycled or discharged as waste water.
Halogenated solvents can be used to dissolve/dilute the contaminants from the synthetic resin material. Again, usable synthetic resin material will be obtained by this process if the solvents do not extract essential components from the synthetic resin material. The halogenated solvent solutions will require distillation to recover the contaminants and recycle the solvents. In general, it is difficult to fully reclaim usable contaminants (such as oil) from the distillate. Furthermore, many halogenated solvents are ozone depleting compounds and potential health hazards to humans, and therefore their use and release into the environment are under regulation and close scrutiny by federal and state governments.
Combustible or flammable solvents may be used to dissolve and/or displace the contaminants from the synthetic resin material. Usable synthetic resin material can be generated by this method if the solvents do not extract essential components from the synthetic resin material. The combustible or flammable solvent solutions will require distillation to recover the contaminants and recycle the solvents. Only distillation equipment suitable for combustible or flammable solvents may be used and even then fire safety concerns will be significant. As in the case of the use of halogenated solvents, the contaminant may not be fully recoverable from the distillation.
Accordingly, there is a need for an improved system and method for removing contaminants from synthetic resin material containers. More particularly, there is a need for a system and method that will produce essentially contaminant-free synthetic resin material in an environmentally safe and economical manner.